Fiber optic device with enhanced resistance to environmental conditions and method

ABSTRACT

A method for producing fiber optic devices having improved intrinsic resistance to external environmental conditions and a fiber optic device made my the method are disclosed. The fabrication method produces an optic device that is treated with deuterium. The method includes a step for treating and/or making optical devices in the presence of a flame produced by the combustion of deuterium gas or a mixture including deuterium.

CROSS REFERENCE OF RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/160,165, filed Jun. 4, 2002, now U.S. Pat. No. 6,741,774,which is herein incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to fabrication of fiber optic devices, andmore particularly to a fabrication method that produces fiber opticdevices having improved intrinsic resistance to external environmentalconditions.

BACKGROUND OF THE INVENTION

The widespread and global deployment of fiber optic networks and systemsmandates that fiber optic devices and components operate reliably overlong periods of time. This mandate imposes stringent performancerequirements on various fiber optic devices and components that are usedin such networks and systems. In this respect, since fiber optic devicesand components are expected to operate reliably for decades or more,prior to qualification for use, such components are typically subjectedto an array of mechanical and environmental tests that are designed tomeasure their long term reliability.

Guarantees of long term performance become especially crucial inapplication where the cost of failure is very high (e.g., submarineapplications.) One of these tests is a damp/heat soak test, where afiber optic device or component is exposed to elevated temperature andhumidity conditions (typically 85° C. and 85% relative humidity) for anextended period of time. Fiber optic couplers exposed to such conditionsmay exhibit a gradual drift in insertion loss. Eventually, this driftwill cause a coupler to fail to meet its assigned performancespecifications.

It is believed that the primary cause for the above-identified drift iswater vapor or some component, constituent or by-product of water vapordiffusing into the exposed core glass of the coupler and changing thecoupler's index of refraction.

In an attempt to prevent migration of moisture into the coupling region,it has been known to provide improved packaging for optic couplers, withthe goal of eliminating exposure to external environment. For example,prior art approaches have included packaging fiber optic couplers andother fiber optic components inside a metal tubing and sealing the endsof the tubing with a polymeric material, such as a silicon-basedmaterial or epoxy. These types of packaging have not proved successfulin preventing the aforementioned problem.

Other prior art approaches have focused on reducing the introduction ofwater vapor during the manufacturing process. These attempts include theuse of heat sources, such as a solid state heaters alone, that introduceless hydrogen/water during fabrication of a coupler, than is introducedusing an “open flame” heat source. However, these attempts have alsofailed. Such approaches are deficient because it has been discoveredthat the introduction of water and water related species duringfabrication is not a major cause of long-term drift of opticalproperties under damp heat accelerated aging conditions. See Maack et.al, Confirmation of a Water Diffusion Model for Splitter Coupling RationDrift Using Long Term Reliability Data. See also, Cryan et al., LongTerm Splitting Ration Drifts in Singlemode Fused Fiber Optic Splitters,Proc. Nat. Fiber Opt. Eng. Conf. Jun. 18-22, 1995.

SUMMARY OF THE INVENTION

One embodiment of the invention provides a method for forming an opticdevice that includes the step of treating a segment of the optic deviceusing a deuterium process. Preferably, the deuterium process includestreating the segment in the presence of a flame produced by combustionof deuterium gas. Preferably, a chemical can be added to the deuteriumgas. Preferably, oxygen can be added to the deuterium gas.

In a different embodiment, the method further includes the steps ofmaintaining a first optic fiber and a second optic fiber proximate toone another along the segment, and fusing together the segment to form acoupling region using the deuterium process. The first optic fiber andthe second optic fiber can have different propagation constants. Adiameter of the first optic fiber can be modified to change thepropagation constant associated therewith. The diameter of the firstoptic fiber can be modified by heating the first optic fiber whilestretching the first optic fiber to reduce the diameter of alongitudinal segment thereof. Preferably, the heating includes producinga flame by combustion of deuterium gas.

Another preferred embodiment of the invention provides an optic devicethat includes at least one segment treated by a deuterium process.Preferably, the deuterium process includes heating the at least onesegment in the presence of a flame produced by combustion of a mixtureincluding deuterium gas. Preferably, the optic device exhibits no highexcess loss in the E-band portion of the CWDM spectrum. For example, theoptical device exhibits no high excess loss near 1380 nm of the CWDMspectrum.

In another embodiment, the invention provides an optic device includingat least two optic fibers having respective longitudinal segments, inwhich the longitudinal segments are fused together by a deuteriumprocess. The optic device exhibits no high excess loss in a portion ofthe CWDM spectrum.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take physical form in certain parts and arrangement ofparts, a preferred embodiment of which will be described in detail inthe specification and illustrated in the accompanying drawings whichform a part hereof, and wherein:

FIG. 1 is a schematic diagram of a preferred embodiment of an opticalfiber before stretching.

FIG. 2 is a schematic diagram of a preferred embodiment of an apparatusused to stretch an optical fiber.

FIG. 3 is an enlarged schematic diagram of a preferred embodiment of anoptical fiber after a pre-taper operation has been performed.

FIG. 4 is an enlarged isometric view of a preferred embodiment of anapparatus and a coupler.

FIG. 5 is a graph showing change in splitting loss over time.

FIG. 6 is a graph showing median time to failure for various opticaldevices.

FIG. 7 is a chart showing probability distributions of rates of changeof splitting loss at 85° C./85% RH.

FIG. 8 is a table including data from TTF experiments.

FIG. 9 shows a typical wavelength-dependent insertion loss of standardGould 50% WICs.

FIG. 10 is a typical wavelength-dependent insertion loss of deuteriumGould 50% WICs.

FIG. 11 shows the wavelength-dependant loss of a 2-channel CWDM couplerfabricated with the conventional hydrogen torch method.

FIG. 12 shows the wavelength-dependant loss of a 2-channel CWDM couplerfabricated with the improved deuterium process of the invention.

DETAILED DESCRIPTION OF THE INVENTION

In the art, the term “optic device” or “optical device” generally refersto active elements or apparatus, whereas the term “optic component” or“optical components” generally refers to passive elements or apparatus.The present invention is applicable to both fiber optic devices andfiber optic components. Accordingly, as used herein, the term “opticdevice(s)” or “optical device(s)” shall refer both to optic devices andoptic components.

Furthermore, it should be appreciated that while the present inventionis described herein with particular reference to fiber optic couplers,it is contemplated that the present invention is applicable to otheroptic devices.

As is well known to those skilled in the art, a fiber optic coupler is adevice that passively splits or combines light between two or moreoptical fibers. An evanescent-wave coupler is one in which opticalenergy is transferred from one optical fiber to another by virtue of theelectromagnetic field overlap between the two cores of the fibers. Sincethe evanescent field of an optical fiber is an exponentially decayingfield, the cores of the two fibers must be brought into close proximity.

One common method for constructing evanescent-wave couplers is with atechnique known as fused biconical taper (FBT). In fused biconicaltaper, couplers are fabricated by heating two optical fibers until theycoalesce into a composite waveguiding structure. While the fibers arebeing heated, they are slowly stretched and tapered. This causes thelight in the fiber to spread out far enough into the composite structurewhere it can be coupled to the other fiber.

Any number of optical fibers can be coupled together using the FBTtechnique. In addition, the various optical fibers that are coupled canbe similar or dissimilar to one another. For example, one or more of thefibers can have different intrinsic propagation constants. In othercases, one or more of the fibers can also be pre-tapered or notpre-tapered. In other cases, the various fibers include a mix ofdifferent propagation constants and pre-tapering. Generally, thedisclosed method of fabricating an optical device can be used regardlessof the number and/or characteristics of any of the fibers involved.

It has long been known that the wavelength dependence of a single-modecoupler could be modified by fabricating the coupler with fibers havingdifferent propagation constants. A mismatch in the propagation constantsof the two fibers that comprise the coupler can be simply introduced bypreselecting two fibers having different propagation constants. However,since all fibers differ to some extent, successful results with oneparticular pair of fibers will not ensure similar results with anotherpair.

Because of the limitations associated with pre-selecting two fibershaving different propagation constants, pre-tapering one or more of theoptical fibers can be used to change the propagation constant of one ormore of the fibers. In this way, wavelength flattened couplers andwavelength independent couplers can be made. Also, pre-tapering can alsobe used when manufacturing devices with intentionally high wavelengthdependence, such as WDMs.

In one example, a method of making a single-mode evanescent-wave couplerhaving reduced wavelength dependence may be summarized by the followingsteps:

-   -   (a) providing first and second single-mode optical fibers having        substantially identical propagation constants;    -   (b) modifying the diameter of the first optical fiber, e.g., by        heating the first optical fiber along a first longitudinal        segment thereof while stretching the first optical fiber-to        reduce the diameter of the first longitudinal segment, the        reduced diameter being substantially uniform along the first        longitudinal segment (referred to as “pre-tapering”);    -   (c) maintaining the first and second optical fibers in parallel        juxtaposition with one another along a portion of the first        longitudinal segment; and    -   (d) fusing together the portions of the first and second optical        fibers maintained in parallel juxtaposition to form a coupling        region.

A detailed description of the foregoing method is found in U.S. Pat.Nos. 4,798,438 and 4,632,513. These patents are incorporated herein byreference in their entirety.

A single-mode, evanescent-wave coupler is fabricated using twosingle-mode fibers. Each fiber has a core and cladding region. In manyinstances, the cladding region comprises two concentric cladding layershaving different indices of refraction. The inner cladding layer has anindex of refraction lower than that of the core of the fiber. The outercladding layer, sometimes called the substrate, has an index ofrefraction greater than the inner cladding layer but not necessarilyequal to the index of refraction of the core. This type of fiber iscommonly called “depressed cladding” fiber by those skilled in the art.It should be noted that other types of fibers do not have an outercladding layer or substrate having a relatively high index ofrefraction. These fibers are referred to as “matched cladding” fibers.Again, this is just one example of a coupler than can be made.

Referring now to the drawings where the illustrations are for thepurpose of disclosing the preferred embodiment of the invention only,and not for the purpose of limiting same, an exemplary method forfabricating an optical device in accordance with the present inventionwill now be described.

FIG. 1 is a schematic diagram of a side view of an optical fiber.Optical fiber 100 includes a section 102. In some cases, this section isabout three to four centimeters, but section 102 can be longer orshorter. Optical fiber 100 preferably includes a protective buffer layer108 and in section 102, this protective layer 108 is preferably removed.Many different well known methods can be used to remove protective layer108, including mechanical or chemical techniques. The exposed section102 of fiber 100 is then preferably chemically cleaned and rinsed. Aresultant fiber 100 is shown in FIG. 1 having a buffered region 104 andexposed region 106. Notice that buffered region 104 includes protectivelayer 108.

Generally, more than one fiber can be used to construct a fiber opticdevice, so the procedure for removing the protective layer of a fibercan be used on the appropriate fibers.

FIG. 2 is a schematic diagram of an apparatus 200 for pre-tapering andstretching optical fiber. Apparatus 200 includes a base 202 and a firstmoving stage 204 and a second moving stage 206. Preferably, disposedbetween first and second stages 204 and 206, respectively, is a heatingelement 208. For purposes of description, first and second stages 204and 206 are disposed along a longitudinal axis of base 202. Heatingelement 208 is preferably capable of motion in many differentdirections. For example, heating element 208 can move bothlongitudinally, that is, towards either the first 204 or second stage206, and heating element 208 can also move laterally, that is,perpendicular to the longitudinal direction.

First and second stages 204 and 206 are capable of moving. In theembodiment shown in FIG. 2, first stage 204 can move towards and awayfrom heating element 208 and also towards and away from second stage206. Likewise, second stage 206 can move towards and away from heatingelement 208 and first stage 204. First stage 204 includes a firstgrasping portion 210 and second stage 206 includes a second graspingportion 212. First and second grasping portions are designed to hold andretain an optical fiber 214.

Because of this arrangement, first stage 204 and second stage 206 areable to retain one or more fibers between them and their motion can beused to affect the retained fibers. In one example, where pre-taperingof one or more of the fibers is desired, the diameter of fiber 214 maybe modified by mounting fiber 214 onto moveable stages 204 and 206 andheating a portion of fiber 214 with heating element 208. A movable gastorch 208 that provides a flame is preferably used as heating element208.

While heating element 208 moves with respect o fiber 214, first stage204 and second stag 206 are slowly moved in opposite directions, in thiscase, away from each other, in order to stretch fiber 214 and reduce itsdiameter. This heating process is also referred to as a “flame brushprocess.” Any time a torch flame is applied to fiber, deuterium can beused as the fuel for the flame. This includes the pre-taper processdiscussed above. It is possible to use regular hydrogen for the fuel inthe pre-taper operation and then use deuterium for other stages of themanufacturing process. However, it is preferred that deuterium is usedas the torch fuel for all of the manufacturing process steps.

A typical profile of fiber 214 after being stretched and heated in thismanner is shown in FIG. 3. Fiber 214 includes a heated section 302 thathas a substantially constant yet reduced diameter 304 over a substantiallength. Fiber 214 also includes a first un-stretched portion 308 and asecond un-stretched portion 310. Heated section 302 gradually tapers upto the original fiber diameter 306 of un-stretched portions 308 and 310.The final diameter of fiber 214 in the heated region 302 is controlledby the amount fiber 214 is stretched. In some cases, a uniform relativemotion between fiber 214 and heating element 208 (see FIG. 2) is used toobtain a constant fiber diameter along the heated section 302 of fiber214. In this way, a pre-tapered fiber 214 that has been treated withdeuterium is made.

In an alternative method to the stretching process described above, thediameter of a fiber cladding and core may be modified in accordance withan etching process. Although a variety of known etching techniques maybe used, one suitable etching technique is a heated etching technique.In this technique, a fiber is placed in close proximity to an etchingstation which is heated by a thermoelectric module. An amount ofetchant, usually a drop or so, is placed on top of the etching stationto etch a longitudinal portion of the fiber. After the fiber has beenetched to the desired diameter, the fiber is rinsed with water toprevent further etching.

FIG. 4 shows another embodiment of the present invention where multiplefibers are coupled. Although, for clarity, only two fibers are shown inthe example shown in FIG. 4, any number of fibers can be coupled usingthis process. Embodiments with more than 2 fibers are certainlyenvisioned. The principles of the invention can be applied to situationswhere any time N number of fibers are drawn while a torch flame isapplied. For example, U.S. Pat. No. 5,355,426, assigned to the sameassignee as the present invention and which is herein incorporated byreference in its entirety, teaches an M×N coupler. The present inventioncan be used to make those M×N couplers disclosed in U.S. Pat. No.5,355,426, as well as any other coupler having any number of coupledfibers.

Returning to FIG. 4, a first fiber 402 and a second fiber 404 arepositioned proximate one another and retained by grasping members 410and 412. Grasping members 410 and 412 can be any device that is capableof securely retaining and holding optical devices. Preferably, graspingmembers 410 and 412 are mounted to movable stages as shown in FIG. 2. Inthe embodiment shown in FIG. 4, first and second fibers 402 and 404 areinitially wound together to form a coupling region 406.

With reference to FIG. 4, fibers 402 and 404 are preferably maintainedproximate to one another as coupling region 406 is heated and formed. Inan exemplary embodiment, fibers 402 and 404 are maintained in paralleljuxtaposition. Coupling region is fused in order to form a coupler. Inthis regard, fusion occurs by heating coupling region 406 while graspingmembers 410 and 412 stretch fibers 402 and 404. It should be appreciatedthat fibers 402 and 402 may be twisted together along portions of theirlength prior to heating and stretching.

In accordance with an embodiment of the present invention, the heatingsource is preferably a gas torch heat source 414, as described above.However, in accordance with the present invention, heat source 414 usesdeuterium (D₂) gas as a fuel supply 416 to produce a flame 418, as willbe explained further below. Heat source 414 can be moved about couplingregion 406 while fibers 402 and 404 are in axial tension. Heat source414 can be applied until fibers 402 and 404 are fused togetherthroughout the desired length of coupling region 406. Accordingly, adeuterium treated optic coupler is produced.

It should be understood that the coupler fabrication method describedabove is exemplary, and that alternative methods of fabricating couplersusing a heat source are well known to those skilled in the art. Thepresent invention is suitable for use in connection with thesealternative fabrication methods, wherein the heat source is suitablymodified to provide a flame produced by the combustion of deuterium gas.

Furthermore, it should be understood that the fibers being heated andfused to form a coupler may include identical fibers, for example,having the same propagation constants, or the fibers can be mismatchedfibers, for example, having different propagation constants. Again, thisheating method, that uses deuterium as its fuel supply, can be usedregardless of the number, characteristics, and/or the similarities ordifferences among the various fibers that are coupled.

In accordance with the present invention, the conventional gas, usuallyhydrogen gas (H₂), that is used as a fuel supply in gas torch heatsource to generate a flame, is replaced with deuterium (D₂) gas. A flameis produced by the combustion of deuterium gas, rather than theconventional gas, usually hydrogen gas. Deuterium, being a nuclearisotope of hydrogen, is for all practical purposes chemically similar tohydrogen. However, deuterium is heavier than hydrogen, and variousmodifications can be made to the manufacturing process to accommodatethe slight weight difference between hydrogen and deuterium. Forexample, the gas flow rate for the deuterium gas can be modified fromthe gas flow rate used for hydrogen gas to optimize combustion, andachieve a suitable pull signature. In some embodiments, a mixture ofdeuterium and another gas is used.

In one, embodiment, a deuterium flame is applied at room pressure (˜1atm) and room temp. (˜20 C). Flow rate of deuterium gas is around 215sccm for a standard wavelength flattened 50% coupler, but will vary fromdevice to device. Oxygen, as well as other elements, may also be addedas a torch fuel as the recipe requires.

Generally, most typical devices are made by supplying hydrogen only tothe torch. As indicated in other portions of this disclosure, a typicalflow rate would be 215 sccm deuterium. Since no oxygen is supplied tothe torch as a fuel, this can be referred to as a 100% deuteriummixture, but of course ambient oxygen is consumed in the combustion andambient oxygen participates in the combustion process.

In other embodiments, oxygen is supplied to the torch. This can be a wayof controlling flame temperature and size. Oxygen can also be suppliedto control the completeness of the combustion. And, oxygen can besupplied to control the rate of combustion as well.

The following is one embodiment where oxygen is added to the deuteriumfuel. A certain kind of microcoupler is typically pulled with 85 sccmhydrogen and 30 sccm oxygen.

Another embodiment where oxygen is added to the deuterium is a kind ofcoupler that employs an 80 micron payout fiber. (A reduced claddingfiber, RC 1300). The recipe for this involves an elaborated series ofsteps in which the hydrogen/oxygen mixture is varied greatly.

In an initial “prefuse” step, the D₂/0₂ mixture is set to 70 sccm/250sccm (22% D₂ by volume). After the torch has been placed under thefibers, the flow are settings are changed to 124 sccm D₂/250 sccm O₂(33% D₂ by volume, with higher total flow rate).

After this initial “prefuse”, the coupler is pulled with 90 sccmdeuterium, with no oxygen.

These examples illustrate the wide range of possible D₂/O₂ mixtures. Notonly do the percentages vary widely, but also the total flow rates.Also, oxygen can be added to only certain steps in the manufacturingprocess and omitted in other steps.

Furthermore, in any process where hydrogen is conventionally used,deuterium can be substituted to make a passivated version of the device.And, in addition, other elements or compounds can also be added ifdesired. Also, oxygen can be replaced with other chemicals if desired.

In accordance with the present invention, control parameters forstretching a fiber during coupler fabrication may be modified fromstandard settings wherein a hydrogen gas fuel supply is used. Forinstance, in the case of fabrication of 50% wavelength-flattened opticcouplers, the primary modification of the control parameters is thepre-taper settings.

In this regard, optic couplers produced using a deuterium gas fueledheat source (referred to herein as “deuterium couplers”) require thatthe pre-tapered fiber have a significantly greater degree of pre-taperthan couplers fabricated using a hydrogen gas fueled heat source. It isbelieved that the “deuterium heating” method may effect the refractiveindex of the fibers differently than the standard “hydrogen heating”method.

As shown below, preliminary observations indicate that using deuterium(D₂) gas as a fuel supply for the heat source effectively doubles themedian “time to failure” (TTF) of devices in 85° C./85% relativehumidity (RH) environmental testing.

The present invention will now be further described by way of thefollowing examples:

EXAMPLE 1

Deuterium Passivation Damp Heat Aging Experiment

Twenty-five (25) 50% wavelength flattened optic couplers (WFC) weremanufactured using a deuterium gas fueled heating source, with the goalof attaining passivation (i.e., to treat in order to reduce the chemicalreactivity of its surface) of the couplers to damp heat aging. Thesedeuterium couplers, along with eleven (11) 50% WFCs produced using thestandard “hydrogen heating” method, were aged at 85° C. and 85% relativehumidity (RH) for approximately 2000 hours and 1265 hours, respectively.The eleven standard couplers act as a control group.

Optic Fiber Parameters for 50% WFC Deuterium Coupler

-   -   D₂ flow rate: 215 sccm    -   O₂ flow rate: 0 sccm    -   Stage separation: 40 mm    -   Pre-taper torch velocity: 22 mm/min    -   Pre-taper flame brush width: 11 mm    -   Pre-taper right stage velocity: 2.75    -   Pull torch-velocity: 36 mm/min    -   Pull flame brush width: 6.5 mm    -   Pull left stage velocity: 2.5 mm/min    -   Pull right stage velocity: 2.5 mm/min    -   Pull after stop jump: 3.5%    -   Torch height: 10.5 mm    -   Pull distance: 7.16 mm (average)    -   Pre-taper fiber diameter: 117.85 microns

Optic Fiber Parameters for 50% WFC Standard Coupler:

-   -   D₂ flow rate: 215 sccm    -   O₂ flow rate: 0 sccm    -   Stage separation: 40 mm    -   Pre-taper torch velocity: 22 mm/min    -   Pre-taper flame brush width: 11 mm    -   Pre-taper right stage velocity: 1.65 mm/min    -   Pull torch velocity: 36 mm/min    -   Pull flame brush width: 6.5 mm    -   Pull left stage velocity: 2.5 mm/min    -   Pull right stage velocity: 2.5 mm/min    -   Pull after stop jump: 3.5%    -   Torch height: 10 mm    -   Pull-distance: 7.75 mm (average)    -   Pre-taper fiber diameter: 120.56 microns

Procedure:

Coupling ratio (CR) data were processed to correct for artifacts of themeasurement system, specifically the appearance of piecewisediscontinuities. Times to failure (TTF) were extrapolated from a linearleast squares fit to data in cases where the device did not exhibitfailure within the duration of the test. Failure criterion is a changein CR of 0.2 dB.

Results:

FIG. 8, includes a table that includes a ranking of TTF (median time tofailure) for optic couplers fabricated using deuterium (D₂) gas as aheat source fuel supply (“deuterium couplers”), and for optic couplersfabricated using conventional hydrogen gas as a heat source fuel supply(“standard couplers”)

It is observed that the median time to failure (TTF) for the deuteriumcouplers is approximately 3,300 hours. In contrast, the median time tofailure for the standard couplers is approximately 1000 hours. Thefraction of deuterium couplers with TTF>2000 hrs is 18/25, while thefraction of standard couplers with TTF>2000 hrs is 2/11. Failurecriterion is a change in splitting loss of 0.2 dB or greater.

FIG. 5 is a graph showing the average splitting loss change in decibels(dB) versus time, in hours, in a high temperature, high humidityenvironment, for a number of control couplers 502 and a number ofdeuterium treated couplers 504 in accordance with the present invention.The deuterium treated couplers 504 are significantly more tolerant ofadverse environmental conditions. The deuterium treated couplers 504were able to perform with a splitting loss change of less than 0.20 dBfor more than three times the duration of a conventional optical coupler502. This is also shown in FIG. 6, which shows a bar graph comparing themean time to failure for a control group 602 and a deuterium treatedgroup 604.

FIG. 7 is a chart showing probability distributions of rates of changeof splitting loss at 85C./85% RH for both control 702 and deuterium 704passivated couplers. These distributions illustrate the advantage of thedeuterium passivated couplers over the control devices. As clearlydemonstrated in FIG. 7, the rates of splitting loss change for theformer is reduced by a factor of approximately 3.3 with respect to thelatter. This both increases the median time to failure (MTF) by a factorof approximately 3.3 and also results in a narrower distribution inaging rates.

Effect on E-Band OH (Water) Peak Attenuation

The deuterium coupler manufacturing process of the invention hasfavorable effect on E-band OH peak attenuation. FIG. 9 shows a typicalwavelength-dependent insertion loss of standard 50% WavelengthIndependent Coupler (WIC). FIG. 10 is a typical wavelength-dependentinsertion loss of deuterium 50% WIC. Note the pronounced water peak atabout 1380 nm in the standard component shown in FIG. 9. This feature isabsent (see FIG. 10) when the deuterium process is used.

The ITU-T G.694.2 standard specifies the Metro Coarse WavelengthDivision Multiplexing (CWDM ) Wavelength Grid as individual 20 nm widebands spanning the total wavelength range of 1260-1625 nm. An importantapplication of CWDM is broadband access networks that use less expensivelight sources and equipment. The 1360-1460 nm portion of the CWDMspectrum is designated the E-band, which spans five individual CWDMbands. Fiber manufacturers are addressing the CWDM network applicationby manufacturing “low water-peak” optical fiber which would permit useof the entire wavelength grid, including the E-band.

For applications that require the use of the E-band channels, passivefiber-optic components manufactured with conventional processes would beinadequate due to the presence of a large (about 0.4 dB) attenuationpeak in the 1380-1420 nm range. As indicated in FIG. 9, this attenuationpeak is created by the hydrogen flame process, which raises the OHconcentration in the fused region by a factor of about 10,000 over whatis observed in pristine fiber (about 0.4 dB/km). That the hydrogen torchis the source of this attenuation is verified by the absence of thispeak in components fabricated with the deuterium flame brush process ofthe invention (see FIG. 10).

Consequently, the deuterium process of the invention provides anadditional improvement beyond superior damp heat performance. Thedeuterium process improves performance in the E-band by eliminating thehigh excess loss near 1380 nm. The deuterium process results incomponents that are compatible with optical networks employing low-waterpeak fiber. An example of this type of network would be one thatutilizes full spectrum CWDM (coarse wavelength devision multiplexing)over zero-water peak fiber (ZWPF). This application utilizes all thechannels describe in the ITU-T G.694.2 specification, including those inthe 1380 nm region.

FIG. 11 shows the wavelength-dependant loss of a 2-channel CWDM couplerfabricated with the conventional hydrogen torch method. The 1390 nmchannel in this device exhibits about 0.7 dB excess loss as comparedwith the other channels. Such excess loss would essentially negate theeffort of employing ZWPF. For comparison, FIG. 12 shows thewavelength-dependant loss of a 2-channel CWDM coupler fabricated withthe improved deuterium process of the invention. The excess loss in the1390 nm channel is clearly absent.

Accordingly, the absence of this excess loss at about 1380 nm to 1390 nmprovides the invention with a competitive advantage over the known useof a hydrogen process in coupler fabrication. It should be noted,however, that while not all fiber manufacturers use a torch, thetorch-based manufacturing hydrogen processes is considered to haveproduced the highest quality fused biconical taper (FBT) devices. Ofcourse, the deuterium process of the invention is superior to thehydrogen process.

The deuterium process of the invention can be considered to be a torchflame brush process. The deuterium process burns deuterium instead ofhydrogen. It should be noted that any torch flame brush process thatdoes not use deuterium would exhibit high water peak loss.

It should be understood that the present invention can be usedregardless of the other particular details for manufacturing opticdevices (e.g., pulling methods, clamping methods, fiber arrangement,etc.) In this regard, the present invention is suitably used inconnection with a wide variety of coupler manufacturing methods andpackaging strategies. Moreover, the present invention may be applied incombination with other techniques for improving reliability andperformance of optic devices.

Other modifications and alterations will occur to others upon theirreading and understanding of the specification. In this regard, itshould be appreciated that the fabrication method of the presentinvention may be suitably used with any heating technique that applies aflame to an optic device during fabrication thereof. It is intended thatall such modifications and alterations be included insofar as they comewithin the scope of the invention as claimed or the equivalents thereof.

The foregoing disclosure of the preferred embodiments of the presentinvention has been presented for purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Many variations andmodifications of the embodiments described herein will be obvious to oneof ordinary skill in the art in light of the above disclosure. The scopeof the invention is to be defined only by the claims appended hereto,and by their equivalents.

Further, in describing representative embodiments of the presentinvention, the specification may have presented the method and/orprocess of the present invention as a particular sequence of steps.However, to the extent that the method or process does not rely on theparticular order of steps set forth herein, the method or process shouldnot be limited to the particular sequence of steps described. As one ofordinary skill in the art would appreciate, other sequences of steps maybe possible. Therefore, the particular order of the steps set forth inthe specification should not be construed as limitations on the claims.In addition, the claims directed to the method and/or process of thepresent invention should not be limited to the performance of theirsteps in the order written, and one skilled in the art can readilyappreciate that the sequences may be varied and still remain within thespirit and scope of the present invention.

1. A method for forming an optic device comprising: treating a segmentof the optic device using a deuterium process, wherein the optic devicehas a first condition where the optic device has a first splitting lossof a certain quantity, wherein the optic device has a second conditionwhere the optic device has a change in splitting loss of less than 2 dBrelative to the first splitting loss, and wherein the second conditionis achieved after 2000 hours in an environment having a temperature ofsubstantially 85 degrees Celsius and a relative humidity ofsubstantially 85%.
 2. The method of claim 1, wherein the deuteriumprocess includes treating the segment in the presence of a flameproduced by combustion of deuterium gas.
 3. The method of claim 2,wherein a chemical is added to the deuterium gas.
 4. The method of claim2, wherein oxygen is added to the deuterium gas.
 5. The method of claim1, wherein the deuterium process includes treating the segment in thepresence of a flame produced by combustion of a mixture includingdeuterium.
 6. The method of claim 1, further comprising: maintaining afirst optic fiber and a second optic fiber proximate to one anotheralong the segment; and fusing together the segment to form a couplingregion using the deuterium process.
 7. The method of claim 6, whereinthe first optic fiber and the second optic fiber have differentpropagation constants.
 8. The method of claim 6, wherein a diameter ofthe first optic fiber is modified to change the propagation constantassociated therewith.
 9. The method of claim 6, wherein a diameter ofthe first optic fiber is modified by heating the first optic fiber whilestretching the first optic fiber to reduce the diameter of alongitudinal segment thereof.
 10. The method of claim 9, wherein theheating includes producing a flame by combustion of deuterium gas. 11.An optic device comprising: at least one segment treated by a deuteriumprocess, wherein the optic device has a first condition where the opticdevice has a first splitting loss of a certain quantity, wherein theoptic device has a second condition where the optic device has a changein splitting loss of less than 2 dB relative to the first splittingloss, and wherein the second condition is achieved after 2000 hours inan environment having a temperature of substantially 85 degrees Celsiusand a relative humidity of substantially 85%.
 12. The optic device ofclaim 11, wherein the deuterium process comprising heating the at leastone segment in the presence of a flame produced by combustion of amixture including deuterium gas.
 13. The optic device of claim 11,wherein the deuterium process comprising heating the at least onesegment in the presence of a flame produced by combustion of a deuteriumgas.
 14. The optic device of claim 11, wherein the optic device exhibitsno high excess loss in the E-band portion of the CWDM spectrum.
 15. Theoptic device of claim 11, wherein the optical device exhibits no highexcess loss near 1380 nm of the CWDM spectrum.
 16. An optic devicecomprising: at least two optic fibers having respective longitudinalsegments, wherein the longitudinal segments are fused together by adeuterium process; wherein the optic device exhibits no high excess lossin a portion of the CWDM spectrum, wherein the optic device has a firstcondition where the optic device has a first splitting loss of a certainquantity, wherein the optic device has a second condition where theoptic device has a change in splitting loss of less than 2 dB relativeto the first splitting loss, and wherein the second condition isachieved after 2000 hours in an environment having a temperature ofsubstantially 85 degrees Celsius and a relative humidity ofsubstantially 85%.
 17. The optic device of claim 16, wherein the portionof the CWDM spectrum includes the 1360 nm to 1460 nm portion of the CWDMspectrum.
 18. The optic device of claim 16, wherein the optical deviceexhibits no high excess loss in 1380 nm to 1390 region of the CWDMspectrum.
 19. The optic device of claim 16, wherein the optical deviceexhibits no high excess loss near 1380 nm of the CWDM spectrum.
 20. Theoptic device of claim 16, wherein the optical device exhibits no highexcess loss near 1390 nm of the CWDM spectrum.
 21. The optic device ofclaim 16, wherein the change in splitting loss is less than 0.5 dB. 22.The optic device of claim 16, wherein the change in splitting loss isless than 0.2 dB.
 23. The optic device of claim 11, wherein the changein splitting loss is less than 0.5 dB.
 24. The optic device of claim 11,wherein the change in splitting loss is less than 0.2 dB.
 25. The methodof claim 1, wherein the change in splitting loss is less than 0.5 dB.26. The method of claim 1, wherein the change in splitting loss is lessthan 0.2 dB.